A known thread delivery device of this type (OS No. 2 312 267) has a thread control element which is constructed as an open hook, which thread control element is supported movably in two positions outside of the thread drum on a stationary support arm and is provided slightly below the withdrawal edge. The movement of the hook from a first position for positive thread delivery into a second position, in which it does not come into contact with a running off thread, is done manually. In the case of a positive thread delivery the hook mouth which is open in the direction of rotation of the drum catches the running off thread, which prior to leaving the drum runs through between the elastic fingers of a brake ring and the withdrawal edge and thus receives an even withdrawal tension. This known thread delivery device operates functionally satisfactorily. However, the open hook has a disadvantage for certain mixed yarns in that a downwardly directed power component acts onto the off-coming thread, so that in the case of mixed yarns, which because of their loose fibers or for other reasons tend to have a strong adhesion between adjacent windings, there exists the danger that the respectively next following winding is also moved downwardly and withdrawn. This causes an overfeeding of yarn.
The purpose of the present invention is to produce a thread delivery device of the above-mentioned type, preferably for positive thread delivery, which permits with simple means for any type of yarns a secure and uniform thread delivery with an even tension.
The purpose is attained inventively by the thread control element constructed as an eyelet, which is closed or can be closed at least opposite the direction of rotation of the off-running thread and is arranged approximately at the height of the withdrawal edge of the drum. This eyelet is mounted on an arm which is relatively rotatably supported on the drum shaft below the drum floor, said arm being rotatably frictionally supported on the drum shaft such that it is moved along by the shaft only when the actual thread tension falls below a desired thread tension so that the friction between the shaft and arm permits the latter to be rotated with the drum. A stop limits the movement of the thread control element opposite the direction of rotation of the drum.
In the inventive device the braking of the movably supported arm assures a constant position at a positive thread delivery, namely at a constant withdrawing speed. In the case of overfeeding or thread breakage, which causes a strong decrease in the thread withdrawal tension, the arm can move along in the direction of rotation of the drum. At the same time the changed position of the arm indicates the breakdown. A further important advantage of the device consists in the stopped thread control element applying a frictional braking action on the off-running thread, so that the brake ring with the elastic fingers is not needed in this embodiment. In the case of a thread withdrawal tension which increases too much, the top prevents moving of the eyelet against the direction of rotation of the drum.
The stop can be advantageously movably mounted relative to the path of the thread control element. The thread delivery device can thus in a simple manner be changed over to an intermittent delivery.
In a preferred embodiment a pawl is provided as a stop, which pawl has an abutting surface at its one end zone, which abutting surface can be overtraveled in the direction of rotation of the drum and has a blocking surface which faces in the direction of rotation of the drum. The blocking surface thereby prevents movement opposite the direction of drum rotation, whereas the thread control element arrives at the abutting surface if in the case of a sudden thread tension drop the eyelet is hauled along with the drum for almost one entire drum revolution.
The pawl can be supported pivotally on a swivel axis which is arranged spaced from its two end zones and can be held in a rest position against a support member by means of a spring which is supported on its end zone which is opposite the abutting surface such that it carries out a swiveling lifting off from the support member upon overtraveling of the abutting surface by the thread control element. The arm which is moved along during a thread tension drop thus moves the pawl automatically from its path and can thus, if necessary, move along with further drum rotations, without which it would be stopped and overstressed.
A further function can be advantageously transferred to the thread control element such that the pawl has associated with it a disconnecting switch which can be operated by the pawl swiveling motion during overtraveling of the abutting surface. Thus switching off after a strong drop in tension is caused on the path through the pawl by the thread control element.